Applied Physics Laboratory
Johns Hopkins University
Laurel, Maryland
This week, science operations moved into high gear as NEAR approaches to within 41000 km of Eros. Images
of Eros were obtained today, yesterday, and the day before. These distant image sequences had three
objectives: to confirm the location of Eros in the sky as seen from the spacecraft, to search for satellites of
Eros, and to measure its brightness variations. We look to see whether Eros is in the expected part of the
sky in order to confirm that NEAR is headed in the proper trajectory — this process is called ‘optical
navigation’. We are also looking to see if Eros has any natural moons of its own. We do not know of any
moons of Eros, but we do know of a few asteroids (such as Ida and Eugenia) that have their own moons. If
Eros has a moon, we surely wish to know about it before we go into orbit. Of course, once NEAR goes into
orbit around Eros, it will become the first artificial moon of an asteroid. Finally, we are measuring the
brightness variations of Eros — we call these ‘lightcurve’ measurements. Eros is an elongated, kidney-bean
shaped object. As Eros rotates, sometimes greater areas are lit by the sun and Eros appears brighter, but
sometimes smaller areas are lit and Eros appears dimmer. Especially large lightcurve variations are
observable when Eros rotates between broadside to the sun and narrow end to the sun — Eros is not in that
geometry now, but will be later this year. We will use our Eros lightcurve observations to refine our knowledge
of Eros’s rotation. The other instrument teams on NEAR have also been busy. The laser rangefinder test
mentioned last week was completely successful. There was a
successful calibration of the near infrared spectrometer — more about that instrument next time!
